Seize Egyptian deity entering Great Britain (4)
I believe the answer is:
grab
'seize' is the definition.
(I know that seize is a kind of hook)
'egyptian deity entering great britain' is the wordplay.
'egyptian deity' becomes 'Ra' (Ra is an example).
'entering' means one lot of letters goes inside another.
'great britain' becomes 'gb'.
'ra' put into 'gb' is 'GRAB'.
(Other definitions for grab that I've seen before include "Seize hold of" , "interest" , "Take quickly" , "Grasp roughly" , "'Seize, snatch (4)'" .)